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flat assembler > DOS > Video memory output

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MIHIP



Joined: 14 Feb 2013
Posts: 137
Video memory output
Hi. How i can realise program, who output to DOS all contents of video memory in symbolic and numeric format? Thx.
Post 19 Jun 2015, 20:03
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DOS386



Joined: 08 Dec 2006
Posts: 1907
Re: Video memory output

MIHIP wrote:
Hi. How i can realise program, who that output to DOS all contents of video memory in symbolic and numeric format? Thx.



VGA 320x200x8bpp memory is at $000A'0000, size 64'000 (320x200).

VGA text memory is at $000B'8000, size up to 8'000 (80x50x2).

VESA LFB is at ... well variable http://board.flatassembler.net/topic.php?t=9738

What are you trying to do ???

_________________
Bug Nr.: 12345

Title: Hello World program compiles to 100 KB !!!

Status: Closed: NOT a Bug
Post 23 Jun 2015, 17:21
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freecrac



Joined: 19 Oct 2011
Posts: 117
Location: Germany Hamburg
Re: Video memory output

DOS386 wrote:

MIHIP wrote:
Hi. How i can realise program, who that output to DOS all contents of video memory in symbolic and numeric format? Thx.



VGA 320x200x8bpp memory is at $000A'0000, size 64'000 (320x200).


For a higher resolution there is additional a bank switching function, for to switch to another 64 KB bank of the video memory pointed at the same memory location at $000A'0000.


Quote:
VGA text memory is at $000B'8000, size up to 8'000 (80x50x2).


Older monocrom display devices use $000B'0000 for textmode.


Quote:
VESA LFB is at ... well variable http://board.flatassembler.net/topic.php?t=9738


Inside of the VESA SuperVGA mode information buffer+28h from the VBE function 4F01h we can get the physical address of the linear frambuffer (pointed somewhere in the 4. gigabyte), but only from a display device with a VBE 2 or VBE 3 bios. More information about the VBE bios can be found in the public und costfree dokument "vbe3.pdf" from vesa.org (need register/login).

But the content of the textmode and the graphical modes will be different interpreted. The content of the textmode are divided into ASCII characters and the forground and background colors of the character.

And the content of the graphical modes represents the color of only one pixel. Exemple 8 bit color modes uses one byte for the color, 15/16 bit color modes uses two bytes for the color and 24 bit modes uses 3 bytes for the color of each colored pixel on the screen.

For the textmode with 4 bit colors and for the graphical modes with 4 bit and 8 bit colors there are additional a color palette.

Dirk
Post 24 Jun 2015, 09:53
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Forthman



Joined: 06 Feb 2012
Posts: 1
Location: France Montauban
Hi,

In Flat Real Mode, you can acces direct VRAM of most VESA cards (all modern cards)

Aera start almost at : D000:0000h or E000:0000h or F000:0000h
Post 01 Jul 2015, 06:09
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DOS386



Joined: 08 Dec 2006
Posts: 1907
> Area Aera start almost at : D000:0000h or E000:0000h or F000:0000h

I have one starting at $4000'0000 (1 Gi) and one starting at $DC00'0000.
Post 12 Sep 2015, 11:08
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